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      <td class="subheader-left"><a href="matlab:open isift">View code for isift</a></td>
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<h1>isift</h1><p><span class="helptopic">SIFT feature extractor</span></p><p>
<strong>sf</strong> = <span style="color:red">isift</span>(<strong>im</strong>, <strong>options</strong>) is a vector of SiftPointFeature objects
representing scale and rotationally invariant interest points in the
image <strong>im</strong>.

</p>
<h2>Options</h2>
<table class="list">
  <tr><td style="white-space: nowrap;" class="col1">'nfeat', N</td> <td>set the number of features to return (default Inf)</td></tr>
  <tr><td style="white-space: nowrap;" class="col1">'suppress', R</td> <td>set the suppression radius (default 0)</td></tr>
  <tr><td style="white-space: nowrap;" class="col1">'id', V</td> <td>set the image_id of all features</td></tr>
</table>
<h2>Properties and methods</h2>
<p>
The SiftPointFeature object has many properties including:

</p>
<table class="list">
  <tr><td style="white-space: nowrap;" class="col1"> u </td> <td>horizontal coordinate</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> v </td> <td>vertical coordinate</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> strength</td> <td>feature strength</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> descriptor</td> <td>feature descriptor (128x1)</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> sigma</td> <td>feature scale</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> theta</td> <td>feature orientation [rad]</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> image_id</td> <td>a value passed as an option to ISIFT</td></tr>
</table>
<p>
The SiftPointFeature object has many methods including:

</p>
<table class="list">
  <tr><td style="white-space: nowrap;" class="col1"> plot</td> <td>Plot feature position</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> plot_scale</td> <td>Plot feature scale</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> distance</td> <td>Descriptor distance</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> match</td> <td>Match features</td></tr>
  <tr><td style="white-space: nowrap;" class="col1"> ncc</td> <td>Descriptor similarity</td></tr>
</table>
<p>
See SiftPointFeature and PointFeature classes for more details.

</p>
<h2>Notes</h2>
<ul>
  <li>Greyscale images only, double or integer pixel format.</li>
  <li>Features are returned in descending strength order.</li>
  <li>Wraps a MEX file from www.vlfeat.org</li>
  <li>Corners are processed in order from strongest to weakest.</li>
  <li>If IM is HxWxN it is considered to be an image sequence and F is a cell
array with N elements, each of which is the feature vectors for the
corresponding image in the sequence.</li>
  <li>The SIFT algorithm is covered by US Patent 6,711,293 (March 23, 2004) held
by the Univerity of British Columbia.</li>
  <li>ISURF is a functional equivalent.</li>
</ul>
<h2>Reference</h2>
<p>
"Distinctive image features from scale-invariant keypoints",
David G. Lowe,
International Journal of Computer Vision, 60, 2 (2004), pp. 91-110.

</p>
<h2>See also</h2>
<p>
<a href="matlab:doc SiftPointFeature">SiftPointFeature</a>, <a href="matlab:doc isurf">isurf</a>, <a href="matlab:doc icorner">icorner</a></p>
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